Palm 680 - Manual (Page 261)

R E G U L A T O R Y I N F O R M A T I O N 255
to believe that hands-free kits reduce risks. Hands-free kits can be
used with wireless phones for convenience and comfort. These
systems reduce the absorption of RF energy in the head because the
phone, which is the source of the RF emissions, will not be placed
against the head. On the other hand, if the phone is mounted against
the waist or other part of the body during use, then that part of the
body will absorb more RF energy. Wireless phones marketed in the
U.S. are required to meet safety requirements regardless of whether
they are used against the head or against the body. Either
configuration should result in compliance with the safety limit.
Do wireless phone accessories that claim to shield the head from
RF radiation work? Since there are no known risks from exposure
to RF emissions from wireless phones, there is no reason to believe
that accessories that claim to shield the head from those emissions
reduce risks. Some products that claim to shield the user from RF
absorption use special phone cases, while others involve nothing
more than a metallic accessory attached to the phone. Studies have
shown that these products generally do not work as advertised.
Unlike “hand-free” kits, these so-called “shields” may interfere with
proper operation of the phone. The phone may be forced to boost its
power to compensate, leading to an increase in RF absorption. In
February 2002, the Federal trade Commission (FTC) charged two
companies that sold devices that claimed to protect wireless phone
users from radiation with making false and unsubstantiated claims.
According to FTC, these defendants lacked a reasonable basis to
substantiate their claim.
What are wireless telephone base stations? Fixed antennas used
for wireless telecommunications are referred to as cellular base
stations, cell stations, PCS (“Personal Communications Service”)
stations or telephone transmission towers. These base stations
consist of antennas and electronic equipment. Because the antennas
need to be high in the air, they are often located on towers, poles,
water tanks, or rooftops. Typical heights for freestanding base station
towers are 50-200 feet.
Some base stations use antennas that look like poles, 10 to 15 feet in
length, that are referred to as “omni-directional” antennas. These
types of antennas are usually found in rural areas. In urban and
suburban areas, wireless providers now more commonly use panel
or sector antennas for their base stations. These antennas consist of
rectangular panels, about 1 by 4 feet in dimension. The antennas are
usually arranged in three groups of three antennas each. One
antenna in each group is used to transmit signals to wireless phones,
and the other two antennas in each group are used to receive signals
from wireless phones.
At any base station site, the amount of RF energy produced depends
on the number of radio channels (transmitters) per antenna and the
power of each transmitter. Typically, 21 channels per antenna sector
are available. For a typical cell site using sector antennas, each of the
three transmitting antennas could be connected to up to 21
transmitters for a total of 63 transmitters. However, it is unlikely that
all of the transmitters would be transmitting at the same time. When
omni-directional antennas are used, a cellular base station could
theoretically use up to 96 transmitters, but this would be very
unusual, and, once again, it is unlikely that all transmitters would be in
operation simultaneously. Base stations used for PCS
communications generally require fewer transmitters than those
used for cellular radio transmissions, since PCS carriers usually have
a higher density of base station antenna sites.
Are wireless telephone base stations safe? The electromagnetic
RF signals transmitted from base station antennas stations travel
toward the horizon in relatively narrow paths. For example, the
radiation pattern for an antenna array mounted on a tower can be
likened to a thin pancake centered around the antenna system. The
individual pattern for a single array of sector antennas is
wedge-shaped, like a piece of pie. As with all forms of
electromagnetic energy, the power decreases rapidly as one moves
away from the antenna. Therefore, RF exposure on the ground is
much less than exposure very close to the antenna and in the path of
the transmitted radio signal. In fact, ground-level exposure from such
antennas is typically thousands of times less than the exposure levels
recommended as safe by expert organizations. So exposure to
nearby residents would be well within safety margins.
Cellular and PCS base stations in the United States are required to
comply with limits for exposure recommended by expert
organizations and endorsed by government agencies responsible for
health and safety. Measurements made near cellular and PCS base
station antennas mounted on towers have confirmed that
ground-level exposures are typically thousands of times less than the
exposure limits adopted by the FCC. In fact, in order to be exposed to
levels at or near the FCC limits for cellular or PCS frequencies an